Typically, a solid oxide fuel cell (SOFC) employs an electrolyte of ion-conductive solid oxide such as stabilized zirconia. The electrolyte is interposed between an anode and a cathode to form an electrolyte electrode assembly. The electrolyte electrode assembly is interposed between separators (bipolar plates). In use, normally, predetermined numbers of the electrolyte electrode assemblies and the separators are stacked together to form a fuel cell stack.
As the fuel gas supplied to the fuel cell, normally, a hydrogen gas generated from hydrocarbon raw material by a reformer is used. In general, in the reformer, a reformed raw material gas is obtained from hydrocarbon raw material of a fossil fuel or the like, such as methane or LNG, and then the reformed raw material gas undergoes steam reforming to produce a reformed gas (fuel gas).
In the steam reforming, water in the amount corresponding to the amount of water vapor used in reforming reaction needs to be supplied. In this regard, instead of the system of supplying the required amount of water from the outside, a water collection system where the exhaust gas produced in power generation of the fuel cell is condensed to achieve perfect circulation (water self-sustaining operation) of the water required for reforming is drawing attention.
For example, in a water collection apparatus of a fuel cell power generator apparatus disclosed in Japanese Laid-Open Patent Publication No. 2006-236598, as shown in FIG. 9, a fuel cell module 3a containing a fuel cell stack 1a and a reformer 2a is provided. Water vapor in the exhaust gas discharged from this fuel cell module 3a is condensed into water by a condenser including a heat collection apparatus 4a and a natural cooling unit 5a, and the condensed water is supplied to the fuel cell module 3a. 
On the downstream side of the condenser, a water tank 6a for collecting water is provided. The water tank 6a supplies water to the fuel cell module 3a utilizing internal water pressure.
Further, in a fuel cell apparatus disclosed in Japanese Laid-Open Patent Publication No. 2008-300058, as shown in FIG. 10, a condensed water tank 1b is provided for storing condensed water produced by heat exchange in a heat exchanger (not shown). A lower end of the condensed water tank 1b is connected to an end of a condensed water supply pipe 2b, and the condensed water supply pipe 2b is connected to the heat exchanger. An upper end of the condensed water tank 1b is connected to a water tank 4b through a tank coupling pipe 3b. As means for processing the condensed water, for example, ion exchanger resin 5b is provided in the condensed water tank 1b. 
Further, as shown in FIG. 11, a waste heat collection system in a solid oxide fuel cell disclosed in Japanese Laid-Open Patent Publication No. 2007-234374 includes a power generation module 4c and a heat exchanger 7c for waste heat collection. In the power generation module 4c, a solid oxide fuel cell 1c and a reformer 2c are provided in a power generation chamber 3c. The exhaust gas discharged from the power generation chamber 3c flows into an internal space 5c, and a circulation water pipe 6c extends through the internal space 5c. 
An outlet port of the condensed water is provided on a lower surface of the heat exchanger 7c for waste heat collection, and a water storage tank 8c is provided at the outlet port of the condensed water. The water stored in the water storage tank 8c is supplied to the reformer 2c of the power generation module 4c of a water pump 9c. 